This invention relates generally to devices for making electrical cross-connections between two sets of conductors. More particularly, this invention relates to connecting devices for use in the communications industry comprising two basic components, namely a wiring block and a connecting block wherein the connecting block is a novel one-piece molded unit.
Wire connecting systems of the type described herein are well known and commercially available from AT&T Technologies as the 110 connector system. 110 type wiring systems are described in several prior patents including U.S. Pat. Nos. 3,611,264; 3,798,587 and 4,118,095.
Wire connecting blocks of the type disclosed in B. C. Ellis, Jr. U.S. Pat. No. 3,611,264, issued Oct. 5, 1971, include an indexing strip (wiring block) and a connecting block, the latter of which carries a plurality of slotted beam contacts. The indexing strip has a plurality of uniform height, spaced-apart teeth along its length. These teeth aid in indexing a first set of conductors. A corresponding plurality of uniform height, spaced-apart teeth carried by the connecting block serve to index a second set of conductors to be cross-connected through the slotted beam contact to the first set of conductors.
A number of improvements to the basic Ellis, Jr. connecting block are disclosed in B. C. Ellis, Jr. et al U.S. Pat. No. 3,798,587, issued Mar. 19, 1974. In the improved version, the spaced-apart teeth in both the indexing strip and the connecting block are staggered in height to facilitate indexing each set of conductors. The Ellis, Jr. et al connecting block is a two-piece structure comprised of matching halves which are secured together following insertion of the slotted beam contacts. However, it has been found that when the connecting block is placed over the indexing strip in cold temperatures, certain stresses are applied to the bond between the two connector parts. These stresses often rupture the bond causing failure of the entire unit.
The problems associated with U.S. Pat. No. 3,798,587 were improved upon in U.S. Pat. No. 4,118,095 issued Oct. 3, 1978 to Berglund et al. As in U.S. Pat. Nos. 3,611,264 and 3,798,587, Berglund et al relates to a wire connecting block which includes a pair of mating connectors (e.g., connecting block and wiring block) for effecting electrical cross-connections between a first set of conductors and a second set of conductors. The first connector indexes the first conductors and holds them in alignment for engagement with a plurality of insulation-penetrating slotted beam contacts carried by the second connector.
Rather than the connecting block comprising two substantially matching halves as in U.S. Pat. No. 3,798,587, in the Berglund et al patent, the connecting block comprises a housing which mates with a discrete anchoring member. The separate anchoring member is a molded piece which acts to position and retain the plurality of spaced beam contacts.
While the use of the housing/anchoring member presents an improvement to the structure of U.S. Pat. No. 3,798,587, the Berglund et al structure nevertheless suffers from certain deficiencies and drawbacks. For example, the connecting block of Berglund et al is still comprised of two discrete molded parts (e.g. the housing member and the anchoring member). The use of the second molded part (e.g., anchoring member) to hold in contacts increases assembly time, inventory, tooling cost and, consequently, the overall cost of the part to the end user. In addition, the second molded part (e.g. anchoring member) may be removed (for example, due to a faulty ultrasonic weld) thereby destroying the connector assembly.
Another detrimental characteristic of prior art connecting blocks described in U.S. Pat. Nos. 3,611,264; 3,798,387 and 4,118,095 results from the requirement that they be continuously end stackable on the wiring block. Because the existing embodiments of prior art designs preserve the contact center spacing to maintain precise alignment with the mating receptacles on the wiring block, the resulting insulating barrier that confines the outside surfaces of the end contacts is thin, and therefore prone to breakage when required to terminate the large wire gauges (e.g., 22 AWG wire) presently in use for data transmission applications. When such breakage occurs on the ends of adjacent connecting block modules, electrical shorting results.
Still another drawback to the Berglund et al connector (as well as the connectors of U.S. Pat. Nos. 3,611,264 and 3,798,587) is the use of a conventional "gapped" insulation displacement contact (IDC) which forms a portion of the bifurcated beam contact.
The most common method of manufacturing insulation displacement type contacts involves a progression of steps which include a gutting operation to produce an elongated cutout followed by a shearing operation which results in a closed gap IDC slot extending from the cutout to the upper edge of the Part. In this state, the preload on the contact beam elements is at or close to zero and may therefore lack sufficient means to inhibit the contamination of the contact surface due to prolonged exposure to airborne moisture and other corrosive elements. A common way to circumvent the problem of contamination of the contact surface is plating. However, to achieve adequate plating thickness in the sheared area required for electrical contact, a gap is provided to insure adequate circulation of plating solution in the IDC slot. This gap is commonly produced by a coining operation just below the wire termination area on the IDC slot. This approach is successful and in wide use among many IDC contact designs including those of the previously listed patents along with those disclosed in U.S. Pat. Nos. 4,295,703; 4,468,079 and 4,140,867.
However, the "gapped" IDC also suffers from certain drawbacks. As mentioned above, the gap between the contact tynes (or beams) is formed during manufacturing, by a coining process at the bottom of the IDC to allow for uniform plating in the region of electrical contact. The effect of this coin is threefold. First, the gap limits the range of wire gages that can be terminated by this contact. Wires with a diameter less than or equal to the width of the gap, will not make contact with adequate force to maintain the required gas tight connection. The IDC is limited to wire gages larger than the IDC slot so that the normal force exerted on the wire is sufficient to accomplish a gas tight electrical connection. Secondly, the gapped IDC limits the use of the contact to solid wire only. When stranded wire is terminated, the wires will tend to separate and line up in the slot upon initial termination or over time. This movement may allow the gapped IDC to close to the preterminated state resulting in intermittent or open connections. Lastly, the gapped IDC, in its unterminated state, has increased exposure to the corrosive effects of air-borne contaminants which mandate the use of a protective coating or plating for most materials. In contrast, the contact surfaces of an IDC slot that is forced closed by sufficient preload is much less susceptable to surface contamination due to its decreased exposure to the elements required to sustain the reactions which result in corrosion or the like.